Whenever Bob Ziller had lunch at Thai Cuisine on Liberty Avenue, he found himself staring at an old washed-out billboard across the street. He stared at that billboard for years until he couldn't take it anymore.

On New Year's Day, 2010, he covered the billboard with "Grand Mere," a mural of his grandmother flying over the avenue.

"I think [my grandmother] would have gotten a kick out of it," he said.

Painted with vibrant colors that pop against the gray Pittsburgh sky and faded brick, the mural embodies the spirit of Louise Nedelec, who immigrated to the United States in the 1920s from France when she was in her early 20s.

"I depicted her flying like a superhero since she was just a young woman when she came here from France," said Mr. Ziller. "I think it takes a lot of courage to move to another country."

"Grand Mere" is a cutout attached to two sheets of chipboard and screwed into the plywood of the billboard. As a nod to his grandmother's cooking skills, she's clutching a rolling pin in one outstretched hand and a wooden spoon in the other.

"She had the most beautiful hands. Her fingers were thick, she had strong, working hands," Mr. Ziller recalls. "In the last decade of her life she was blind, and she gestured with her hands in a kind of delicate way as she spoke."

Like some of his other public work, Mr. Ziller hung "Grand Mere" up when no one was around to object.

"I am not a fan of asking for permission, so I never ask permission. It was just an abandoned billboard, and it was kind of an eyesore," he said.

Originally from New Jersey, Mr. Ziller, 52, lives in Wilkinsburg.

Currently, he is working with fellow artist Laura Jean McLaughlin and the community to make a large mosaic sea creature in Friendship's Octopus Garden.